1. Field of the Invention
The present invention generally relates to a semiconductor device. More specifically, the present invention relates to a chip-size packaged resin-sealed type semiconductor device, and a method of manufacturing thereof.
2. Background Information
In recent years, portable devices represented by notebook PCs, cellular phones, and the like have rapidly become popular, and there are growing demands for much smaller, thinner, and lighter semiconductor devices to be mounted on such portable devices. One key technology that complies with such demands is a high-density packaging technology which includes a CSP (chip size package) and so forth. According to the CSP, the package size can be brought infinitely close to the size of a semiconductor chip. In particular, a W-CSP (wafer level chip size package) is attracting special attention as a technique that realizes an ultimate compact package. In the W-CSP, the molding process is done at a wafer level, and thus the W-CSP is expected to be an effective measure for reducing production costs.
A general structure of a chip-size packaged semiconductor device manufactured by the W-CSP (it is to be referred to as a W-CSP type semiconductor device in the following) includes re-wiring layers connected to electrode pads of a semiconductor chip, contact portions (they can also be called conductor posts) connected to the re-wiring layers, a sealing resin that covers the semiconductor chip at almost the same level with the top surfaces of the contact portions, and electrodes that are formed at the tips of the contact portions. In order to mount a W-CSP type semiconductor device in a mounting substrate, i.e. a printed-circuit board for example, external electrodes of the W-CSP, i.e. spherical electrodes made of solders for example, and connection pads formed on the mounting substrate are joined by melting. In this process, in order to protect the joint parts from possible physical shocks such as falling and vibration, and heat stress that could be caused by temperature difference or the like, a resin, a so called under-fill, is filled up at the interface between the semiconductor device and the mounting substrate.
However, such a method of improving the connection reliability between the semiconductor device and the mounting substrate by filling up the interface with the under-fill requires considerable time for the filling and hardening of the under-fill. This has caused manufacturing costs to increase and productivity to decrease. Taking this into account, various methods have been proposed to improve the connection reliability between the semiconductor device and the mounting substrate without using the under-fill.
For example, inventions that attempted to improve the connection reliability in the chip size package are disclosed in Japanese Patent Application Laid Open No. H10-79362, especially pp. 18-19, FIGS. 19 to 21 (hereinafter reference 1), Japanese Patent Application Laid Open No. 2000-294578, especially pp. 18-19, FIGS. 19 to 21 (hereinafter reference 2), Japanese Patent Application Laid Open No. 2003-197655, especially pp. 18-19, FIGS. 19-21 (hereinafter reference 3), Japanese Patent Application Laid Open No. 2000-216111, especially pp. 3-4, FIG. 2 (hereinafter reference 4), Japanese Patent Application Laid Open No. 2000-216185, especially pp. 4-5, FIGS. 2 and 3 (hereinafter reference 5), Japanese Patent Application Laid Open No. 2000-277682, especially pp. 8-9, FIGS. 1 and 2 (hereinafter reference 6), and Japanese Patent Application Laid Open No. 2000-353766, especially pp. 3-4, FIGS. 1 and 2 (hereinafter reference 7). The aforementioned references are hereby incorporated by reference.
In the semiconductor devices disclosed in the references 1 to 3, a tip part of a projection electrode (equivalent of a contact portion) is exposed from a sealing resin, and this tip part of the exposed projection electrode is connected with a mounting substrate. Since a resin layer that covers the projection electrode is formed during a resin molding process, it is no longer necessary to fill up the under-fill when mounting the semiconductor device on the mounting substrate. Due to this structure, the mounting process can be simplified.
With respect to the semiconductor devices of the references 1 to 3, laser beam processing, etching processing, machine polishing, blast processing, etc. are indicated as a means to expose the tip part of the projection electrode from the sealing resin.
In the semiconductor device introduced in the reference 4, a three-layer film constructed from a nickel plating, a palladium plating, and a gold plating is formed on a top surface of a contact portion. Thereby, junction strength between the contact portion and an external electrode, i.e. a spherical electrode made of solder for example, can be increased.
With respect to the semiconductor device of the reference 4, the sealing resin is formed using a known compression molding method. More specifically, the surface of the semiconductor device is pressed by a metal mold where a sealing film, i.e. a sealing resin, is arranged, and thereby it is sealed with the sealing resin. At this time, the surface of the contact portion is made to be exposed from a sealing resin by having a tip part of the contact portion sunk into the sealing film.
In the semiconductor device introduced in the reference 5, a three-layer film constructed from a nickel plating, a palladium plating, and a solder plating is formed on a top surface of a contact portion. Thereby, junction strength between the contact portion and an external electrode, i.e. a spherical electrode made of solder for example, can be increased.
Moreover, in the semiconductor device introduced in the reference 5, the edge of the solder plating protrudes from the outer surface of the sealing resin, and the interface between the solder plating and a foundation layer is in the inner side from the outer surface of the solder plating. Thereby, a connection part between the contact portion and the spherical electrode can be supported inside a concave structure formed by an inner wall surface of the sealing resin and the nickel plating, which contributes to improving durability of the external electrode.
With respect to the semiconductor device of the reference 5, the sealing resin is formed using a known compression molding method. More specifically, the surface of the semiconductor device is pressed by a metal mold where a sealing film, i.e. the sealing resin, is arranged, and thereby it is sealed with the sealing resin. At this time, the surface of the contact portion is made to be exposed from a sealing resin by having a tip part of the contact portion sunk into the sealing film.
The semiconductor device as introduced in the reference 6 has a double-sided symmetrical structure that is constructed from two semiconductor chips joined at their back side, by which it is made possible to prevent the semiconductor device from being curved due to possible difference between thermal expansion rates of a sealing resin and a semiconductor chip. By this structure, possible curvature of the whole semiconductor device is reduced, and the connection reliability between the semiconductor device and a mounting substrate can be improved.
With respect to the semiconductor device of the reference 6, a sealing resin is formed using the known compression molding method. More specifically, the surface of the semiconductor device is pressed by a meal mold where a sealing film, i.e. the sealing resin, is arranged, and thereby it is sealed with the sealing resin. At this time, the surface of a contact portion is made to be exposed from a sealing resin by having a tip part of the contact portion sunk into the sealing film.
In the semiconductor device indicated in the reference 7, a groove is formed by laser irradiation in a sealing resin surrounding a contact portion, and thereby a spherical electrode made of solder is bonded with a top surface and parts of the sides of the contact portion. By this structure, the junction strength between the contact portion and the spherical electrode can be increased, and the connection reliability between the semiconductor device and a mounting substrate can be improved. Moreover, according to the disclosure of the reference 7, the surface of the contact portion is once exposed by grinding the sealing resin before conducting a laser beam machining.
As described above, various methods have been proposed to improve the connection reliability with respect to a chip size package. However, each of the above-described methods has some problems that will be described in the following.
With respect to the references 1 to 3, the surface of the sealing resin is processed by laser beam processing, etching processing, machine polishing, blast processing, etc. in order to expose the tip of the projection electrode. However, when performing a laser beam machining, etching processing, and blast processing from the state completely covered with the sealing resin, the processing time will become longer. Moreover, although the processing time can be shortened if machine polishing is performed, it is difficult to expose the tip of the projection electrode from the sealing resin with sufficient accuracy by only the machine polishing.
According to the reference 4, a three-layer film constructed from a nickel plating, a palladium plating, and a gold plating is formed at the top surface of the contact portion in order to increase the junction strength between the contact portion and the external electrode. However, the contact portion constructed from copper plating is as thick as 100 μm, and it is supposed that there are considerable individual differences in the heights of the contact portions. Accordingly, variation may be produced in the final height also including the external electrodes formed on the contact portions, and this may cause unevenness in the height of the connection part of the semiconductor device and the mounting substrate. Therefore, stress concentrates locally in the connection part between the semiconductor device and the mounding substrate, and there is a possibility of inducing destruction in the connection part.
According to the reference 5, a three-layer film constructed from a nickel plating, a palladium plating, and a solder plating is formed at the top surface of the contact portion in order to increase the junction strength between the contact portion and the external electrode. However, as with the case of the reference 4, the contact portion formed by copper plating is as thick as 100 μm, and it is supposed that there are considerable individual differences in the heights of the contact portions. Accordingly, variation may be produced in the final height also including the external electrodes formed on the contact portions, and this may cause unevenness in the height of the connection part of the semiconductor device and the mounting substrate. Therefore, stress concentrates locally in the connection part between the semiconductor device and the mounting substrate, and there is a possibility of inducing destruction in the connection part.
Furthermore, according to the reference 5, the connection part between the contact portion and the spherical electrode is made to be supported inside the concave structure formed by the inner wall surface of the sealing resin and the nickel plating, which contributes to improving the durability of the external electrode. This structure may effectively work against some stresses such as heat stress, which is gradually added comparatively. However, this structure does not effectively work against impact stresses such as falling and vibrations, the forces of which are added instantaneously.
According to the reference 6, as with the cases of the references 4 and 5, it is supposed that there are considerable individual differences in the heights of the contact portions. Accordingly, variation may be produced in the final height also including the external electrodes formed on the contact portions, and this may cause unevenness in the height of the connection part of the semiconductor device and the mounting substrate. Therefore, stress concentrates locally in connection part between the semiconductor device and the mounting substrate, and there is a possibility of inducing destruction in the connection part.
According to the reference 7, a groove is formed in the sealing resin surrounding the contact portion, and thereby the spherical electrode made of solder is made to bond with the top surface and parts of the sides of the contact portion. By this structure, the junction strength between the contact portion and the spherical electrode can be increased. However, since the groove is formed by laser irradiation, the processing will take time. Therefore, if a semiconductor device has a multi-pin structure, the method of reference 7 will not be effective or practical enough in terms of manufacturing costs and time.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved method of manufacturing a semiconductor device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.